The present invention relates to a method for coating a flexible belt-shaped support with coating solutions, and more particularly to an extrusion-type coating method used for manufacture of photographic photosensitive materials, magnetic recording media, or the like.
A variety of coating methods such as a roll-type coating method, a bead-type coating method, a slide-coat-type coating method and an extrusion-type coating method are available for applying coating solutions to a flexible belt-shaped support. The coating apparatuses used in practicing these methods are invariably smaller in width than the flexible belt-shaped support being coated. As a result, as shown in FIG. 2, the coated surface of the flexible belt-shaped support 1 has two regions A along its edges which are not coated with the coating solution 2.
Accordingly, in the case where, as in the case of an extrusion-type coating apparatus, the coating solution is applied to the flexible belt-shaped support running with the coating head abutted against it, the coating head may contact the two uncoated regions along the edges of the flexible belt-shaped support because the gap between the coating head and the flexible belt-shaped support is considerably small. As a result, the coating head may scrape the surfaces of the uncoated regions of the flexible belt-shaped support to form shavings, and the shavings thus formed may adhere to the ends of the coating edge of the coating head. Also, foreign matter on the support may be caught by the coating edge of the coating head.
Deposits of shavings and foreign matter at the two ends of the coating edge can push against the two edge portions of the flexible belt-shaped support, as a result of which the thickness of the coating solution applied to the support is not uniform in the widthwise direction of the latter; that is, the layer formed on the flexible belt-shaped support will have a greater thickness in the two edge regions than in the middle portion thereof.
In order to eliminate the above-described difficulty, a coating method has been proposed in Japanese Unexamined Published Patent Application No. 257268/1986 wherein immediately before applying the coating solution to a flexible belt-shaped support, a solvent is applied to the regions of the support which are not to be coated with the coating solution. With this method, both edge portions of the support are prevented from being directly brought into contact with the coating head, scraping of the support is prevented by the lubricating effect of the solvent applied thereto, and foreign matter on the support can be passed and will not be accumulated. Accordingly, the two edge portions of the support are prevented from being pushed upward, and accordingly the difficulty that the layer formed on the support is larger in thickness in the two edge portions is prevented.
However, the coating method proposed in Japanese Unexamined Published Patent Application No. 257268/1986 is still disadvantageous in that, as shown in FIG. 3, due to the presence of the solvent 7 in the regions outside the coating region of the flexible belt-shaped support, the coating solution 2 tends to spread in the widthwise direction of the support, flowing around the two ends of the edge portions of the coating head 3 and along a coating width regulating board 6.
If, during manufacture of a magnetic recording medium or the like, the coating solution 2 spreads to the two edge portions of the support 1 or to the rear side thereof, it will stick to the rolls conveying the support 1, and it may smudge a calendar roll employed in a following surface treatment process. As a result, the support surface can be scratched by foreign matter during the surface treatment, with the result that the magnetic recording characteristics of the medium are disturbed.